The present invention relates to a multi-screen projector, and is particularly concerned with a transmissive screen device to be used for a multi-screen projector.
A multi-screen projector is a projector having an enormous screen composed by arranging n unit projectors in a vertical direction and m unit projectors in a horizontal direction. A multi-screen projector with two rows and two columns of unit projectors is illustrated in FIG. 1. In FIG. 1, each of the reference numerals 1, 2, 3 and 4 denotes a unit projector, and each of reference numerals 5, 6, 7 and 8 a transmissive unit screen.
Conventional multi-screen projectors have been a mere stack of ordinary unit TV projectors for home use which incorporate unit screens. Therefore, a nontransparent structural body has been in existence in the shaded part designated by reference numeral 9, and the shadow due to the nontransparent structural body has been unavoidable in that portion of the enormous screen which is essential for display of images. When a unit screen is about 800 mm wide, the width of the shadow has been about 8 mm or more, i.e. 1% or more of that of the unit screen. Since the pixel size for a unit TV projector is about 0.2% of the width of the unit screen, the above shadow whose width is 1% or more of that of the unit screen is equivalent to about 5 pixels or more.
FIG. 2 illustrates a typical composition of a unit screen with the diagonal about 40 inches. FIG. 2 is an example of a two-sheet composition. To an observer, a Fresnel sheet 11 is at the back and a front sheet 12 in the front. The Fresnel sheet 11, about 3 mm thick, converts the incident light macroscopically diverging which comes from a projection lens behind it into collimated projection light. The projection lens is not illustrated in FIG. 2. The Fresnel sheet, in other words, functions the same way as a convex lens.
The front sheet 12 has the formations of vertical lenticular-stripes 14 and vertical black-stripes 13. The lenticular stripes microscopically diffuse the light in the horizontal direction, namely, increase the horizontal audience coverage angle. A detailed example of its composition is described in the U.S. Pat. No. 4,536,056.
FIG. 3 illustrates a lenticular sheet 16 which vertically diffuses the light. As in FIG. 3, horizontal lenticular-stripes are formed on the surfaces of light incidence and projection of the lenticular sheet so that the light can be microscopically diffused in the vertical direction. The lenticular sheet is used between the Fresnel sheet 11 and the front sheet 12 both illustrated in FIG. 2, so the three sheets composes one whole sheet.
Incidentally, a method of doing without a lenticular sheet 16 has been in use by admixing diffuser elements which microscopically and randomly diffuse the light, for example, particles of SiO.sub.2 with the front sheet in FIG. 2.